1. Field of the Invention
The present invention relates generally to a system and method for the communication of information in binary form, such as computer data, through a transmission medium such as existing AC power supply lines, or any other type of conductive waveguide. More specifically, the system protocol described herein was developed as a specific implementation of a Composite Shift Keying (CSK) communication system.
2. Discussion of the Prior Art
The prior art has generally recognized the need for communicating substantial amounts of information between remote locations in homes or office or industrial buildings, or even between such buildings. This information can be business records and data transmitted between computers, remote terminals, printers and the like, or can be used to control lighting, heating, air conditioning and other variable factors subject to control from a central location in the building.
In many commercial applications, the physical location of computers, such as personal computers and minicomputers, printers, word processors, and other peripheral equipment presents a major problem with respect to the networking of all of the involved components. Running hardwire to connect all of the components and stations is expensive, and also has the disadvantage of creating an immobile system, often in a dynamic office, plant or home environment.
Moreover, since power wiring already exists in many facilities which require local data transmission, reliable data transmission through this medium would produce significant cost savings in both material and the labor saved by not having to run additional cabling.
Techniques for using existing powerline wiring for communication purposes are described, for example, in the following U.S. Pat. Nos. 3,818,481; 3,876,984; 3,944,723; 3,964,048; 4,065,763; 4,106,071; 4,174,517; 4,217,646 and 4,222,035. Typically, the information to be communicated is modulated onto a carrier and the carrier is suitably applied to the electric power line. A receiver device is coupled to the electric power line network at each desired receiving location, and each receiver includes a decoder which typically demodulates the carrier to recover the communicated information. The information generally includes an address which identifies a receiver which is being communicated with, and also includes data information for controlling the remote devices that are coupled to the respective receivers. Filters have been employed to separate frequency of the carrier from the frequency of the electric power signal. Nevertheless, there is often a problem with an intermixture of the various signals on the power lines which may result in distortion of the information desired to be transmitted.
Experience in industrial environments has demonstrated the requirement for a method of digital data transmission which provides multiple redundant error detection without adversely affecting the transmission of data. Electromagnetic and radio frequency interference problems make reliable data transmission difficult with many existing data modulation techniques such as Amplitude Shift Keying (ASK) Frequency Shift Keying (FSK), Phase Shift Keying (PSK), and others.